1. Field of the Invention
The present invention relates to a hold-response-type display device such as a liquid crystal display or an organic EL (electro-luminescence) display.
2. Description of the Related Art
Conventionally, in classifying a display device such as a display for a television receiver set or a personal computer (PC) from a viewpoint of moving image display, the display device is roughly classified into an impulse-response-type display device and a hold-response-type display device. The impulse-response-type display device is a display device of a type in which a brightness response is lowered immediately after scanning as in the case of afterglow characteristic of a cathode ray tube, for example. Further, the hold-response-type display device is of a type in which the brightness based on display data is continuously held until next scanning as in the case of a liquid crystal display, for example.
The above-mentioned hold-response-type display device can obtain favorable display quality with no flickers when a still image is displayed, for example. However, in displaying a moving image, there arises so-called moving image blurring in which a periphery of a moving object is blurred thus giving rise to a drawback that display quality is remarkably lowered. The occurrence of the moving image blurring is attributed to so-called retina image retention in which when a viewer moves his/her sight line along with the movement of the displayed object, the viewer interpolates display images before and after the movement with respect to the displayed image with fixed brightness. Accordingly, in the hold-response-type display device, even when a response speed is enhanced as fast as possible, it is impossible to completely eliminate the moving image blurring. Accordingly, with respect to the hold-response-type display device, for example, there has been proposed a method which approximates a visual effect to a viewer to a corresponding visual effect of the impulse-response-type display device by canceling the retina image retention with updating of a display image at a shorter cycle or with the insertion of a black screen thus reducing a moving image blurring.
A typical example of the display device which is required to perform a moving image display is a television receiver set, wherein scanning frequency of the television receiver set is standardized to 60 Hz in a NTSC method and 50 Hz in a PAL method, for example. Accordingly, when frame frequency of a display image which is formed based on these scanning frequencies is set to 60 Hz or 50 Hz, the frequency is not so high that moving image blurring occurs.
As a technique which updates the display image at a shorter cycle as described above for overcoming the moving image blurring in the television receiver set, there has been proposed a technique which elevates scanning frequency and increases an updating speed of an image by generating display data of an interpolation frame based on display data between frames (hereinafter, abbreviated as an interpolation frame generation method) (for example, see patent document 1).
Further, as a technique which inserts the above-mentioned black screen (black frame), for example, there has been proposed a technique which inserts black display data between display data (hereinafter, abbreviated as black display data insertion method) (for example, see patent document 2).
Patent Document 1: JP-A-2005-6275 (corresponding US patent application: US2004/0101058A1)
Patent Document 2: JP-A-2003-280599 (corresponding US patent application: US2004/0001054A1)
Although the moving image blurring can be overcome by applying the above-mentioned techniques to the hold-response-type display, there has been known that the following drawbacks arise due to the application of such techniques.
In the above-mentioned interpolation frame generation method, the display data of the interpolation frame which originally does not exist is generated. Accordingly, to generate more accurate display data, a circuit scale is increased. On the other hand, when the circuit scale is suppressed, generation errors occur in the display data of the interpolation frame thus giving rise to a possibility that display quality is remarkably deteriorated.
On the other hand, in the method which inserts the black frame, in principle, there arise no generation errors of display data of the interpolation frame. Further, also in view of the circuit scale, the black frame insertion method is advantageous compared to the interpolation frame generation method. However, with respect to the technique which is referred to as the black display data insertion method or a blink backlight method, either method lowers the display brightness in all gradations by an amount corresponding to the black frame. When the brightness of a backlight is increased in the black display data insertion method for compensating for the lowered amount of brightness, for example, the power consumption is increased correspondingly and, at the same time, considerable time and efforts become necessary to cope with the generation of heat. Further, due to the increase of an absolute value of leaking of light in a black display, contrast is lowered. On the other hand, in the blink backlight method, a large current becomes necessary for bringing a light turn-off state to a light turn-on state or a response speed of a visible light differs from each other for every wave lengths due to the difference in fluorescent material thus generating a coloring phenomenon.